GB2269826A

GB2269826A - Drive means for operating working elements of a knitting machine

Info

Publication number: GB2269826A
Application number: GB9317388A
Authority: GB
Inventors: Holger Scheffler; Gert Zeidler; Dietrich Cotte; Sieghardt Uhlig; Dr Johannes Barth
Original assignee: WIRKBAU TEXTILMASCH GmbH
Current assignee: WIRKBAU TEXTILMASCH GmbH
Priority date: 1992-08-21
Filing date: 1993-08-20
Publication date: 1994-02-23
Anticipated expiration: 2013-08-20
Also published as: DE4227758A1; GB9317388D0; IT1272522B; ITMI931839A1; ITMI931839A0; GB2269826B; DE4227758C2

Abstract

In a knitting machine having working elements (2, 201, 202) reciprocally driven between defined positions parallel to a needle bar (1) by an aynchronous servomotor (46) actuated by control units (5, 6), the servomotor (46) has a toothed drive wheel (425) meshing with a toothed belt (41) which also meshes with a toothed rack (22) connected to the elements. The belt (41) may have teeth on both sides as shown or on one side only. The driving units for respective thread guide rails (21) may be staggered in the drive direction. <IMAGE>

Description

2269826 DRIVE MEANS FOR OPERATING WORKING ELEMENTS OF A KNITTING MACHINE

The invention relates in general to knitting machines and, more particularly, to a drive means for actuating working elements capable of reciprocating movement between defined Dosi4Cions parallel to a needle bar- t A drive means of the aforementioned tvue for flat knittina machines is known from DE-22 57 224. In this case, the drive means comprises a servomotor actuated by a program control unit with target position signals which transmits rotational movement to a toothed rack. The bars or rails carrying the working elements, e.g. thread guides, are then displaced by strokes of different magnitude in synchronisation with the working rhythm of the machine by means of the motor following the preset program. In one embodiment the drive motor is shifted directly by a corresponding number of angle steps by means of coded pulses from the control unit. These angle steps are very small. They are substantially further reduced by corresponding reducing gears. This permits precise positioning of the thread guides between needles arranged closely adjacent to one another. This type of control is unfavourable, because when a thread guide bar or rail encounters a non-programmable resistance during a 2 stroke, one or several steps are not executed by the motor. Accumulation of these steps leads inevitably to collision of the thread guides - i.e. eye-Dointed needles - and the needles. Eliminating of this problem is verv work-intensive, causes corresponding machine shutdowns and is associated with hiah costs for re-olacement of a large number of Darts.

To avoid this disadvantage, the same patent specification DE-2257224 proposes that a coding disc should be Drovided on the axis of the drive motor, which, in association with a sensor, detects the actual steD motion of the motor and actuates automatic reset bv means of a control circuit. Such a resetting device using command values predetermined by the program transmitter allows satisfactory programmed staggered movement of the working elements along the needle bar to be achieved with high precision and adequate reliability. Problems still occur with this control means, above all, when the machine is operated at different speeds. The servo-or stepping motors are constantly moved according to a uniform program corresponding to their motor characteristics and the predetermined target position signals. Consequently, there are particular difficulties associated with the use of this control means in flat weft knitting machines, inter alia, in which the

3 rotational speeds of the motors are to be controlled differently depending on the respective working width and/or on the working steps to be executed.

To solve this problem DE-33 30 150 proposes a drive means with a controlled servomotor. The servomotor is controlled on the basis of a correcting variable which is proportional to the difference between a predetermined end position and the respective actual position of the working element. The signals permanently detected by corresponding transmitters are evaluated by an electronic control circuit and converted into corresponding corrective signals for the servomotor. Because the drive output of the servomotor is directly proportional to the differential signal, the drive output of the servomotor is very low in the end phase of the stroke of the working element and even small resistances encountered by the working element prevent it from being positioned exactly in its desired end position. This can be counteracted in practice by considerably over-dimensioning of the servomotor. This provides sufficient functional reliability, even at relatively high rotational speeds, in flat weft knitting machines with few thread guides, although it is associated with high cost.

In the case of a large number of thread guides, e.g. in a so-called inlay pattern machine, a 4 correspondingly large number of these over- dimens i oned servomotors must be accommodated. Because of their large dimensions, the distances between the servomotors and the associated working element are increased. Toothed belts, which are selected in that case as transmission elements, cause considerable tolerances in the drive movement because of their elasticitv and this cannot be compensated by the described control means. The load differences, in particular at high speeds, led to different end positions of the working elements.

Machines with such types of drives are also expensive. They have a high energy consumption and may only be operated at a low rotational speed.

An object of the invention is to eliminate these disadvantages.

According to the invention there is provided drive means for a knitting machine with working elements capable of reciprocal movement between defined positions parallel to a needle bar; said drive means comprising an asynchronous servomotor actuated by a programmable control unit providing target position signals to transmit rotational movement to a toothed rack carrying at least one of the working elements and a further control unit which has program stores for computer programs for calculating movement cycles from the target position signal data; wherein the servomotor has a toothed drive wheel meshing with a run of a toothed belt guided between guide rollers or between a guide roller and the toothed wheel parallel to the toothed rack with the toothed belt also meshina with the teeth of said toothed rack.

This arrangement permits shift control triggered by the target position signals in such a way that the working elements reach the defined position exactly in the Dredetermined time with the lowest forces, at the lowest equipment expenditure as well as at high machine rotational speeds- Whilst the specific, program- control led motor ensures optimum movement principles in association with calculable programs, the toothed belt reduces the masses of the transmission elements while ensurina a faultfree transmission of movement and a high service life of the transmission elements. The effects of these measures allow small motors to be used very close to the working elements to be driven. In this way, it is also possible to drive a large number of working elements in a very narrow space, precisely and quickly over paths of optional length. The magnitude of the stroke to be set is solely dependent on the length of the toothed rack.

In one arrangement the toothed belt is only provided with external teeth, and the run of the toothed 6 belt is deflected in the form of a loop between two guide rollers and partly around the drive wheel of the motor between the guide rollers. This transmits high drive outputs with very small toothed rack dimensions and removes the causes of transverse forces.

In an alternative arrangement the toothed belt is provided with internal and external teeth. The internal teeth mesh with the toothed wheel and the external teeth mesh with the toothed rack. The toothed belt is entrained around a guide roller and the drive wheel of the motor. This reduces the exDense for the toothed rack guide.

Preferablv the drive motor and the guide roller or rollers are mounted with the toothed belt on a common mounting plate to form a structural unit. This reduces the production expense as well as allowing for a wide variety of possible drive operations to be achieved in a simple manner. It is desirable to also provide a casing or housing enclosing the toothed rack and this housing can be part of the structural unit. This not only provides greater safety for the operator, but also reduces the risk of fouling and additionally reduces running noise. Preferably additional guidance for the toothed belt can be provided by recesses and rollers in the housing. The use of the structural units according to the invention for thread guide rails in flat weft 7 knittina -_machines allows a very large number of structural units to be accommodated in a verv narrow sDace and for the first time allows manufacture of inlav patterns at high machine rotational speed.

As to the further control unit this mav be an a.c. unit provided with (in addition to the program store) a Process unit, storage for variable operands, an input for receivina information from the first mentioned control unit with Dattern Droarams, an output connected to said drive motor and a return line for receivina anale nulse sequences. This permits textile Darameters to be included in the Drogram calculation and to be taken into consideration, in particular by the input of variable operands.

The working elements can be thread guides or sinker cams and driving sinker cams, by means of structural units as described each of which is mounted on the reciprocating guide rail, reduces the number of transmission elements even under these extremely complicated drive conditions.

The invention will now be described in further det.ail by means of specific embodiments. In the accompanying drawings:

Figure 1 is a schematic overall view of the offset driving of working elements in a flat knitting machine in 8 accordance-with the invention.

Figure 2 is a schematic diagram of an alternative toothed belt driving arrangement; Figure 3 is a schematic diagram of the allocation of the structural units according to the invention to a group of thread guide rails; Figure 4 shows the arrangement of a structural unit for the drive of a sinker cam rail; and Figure 5 is a speed/time graph with control variations for the drive of the synchronous motor.

As shown in Figure 1, a flat knitting machine has at least one - generally vertically movable - needle bar 1, which is responsible for looping in association with other working elements movable relative thereto. Working elements 2 movable parallel to the needle bar 1 are provided for guiding threads and/or for driving sinker cams 202 or cover needles.

The working elements 2 are disposed so as to be longitudinally movable in fixedly mounted supports 3 or on fixedly mounted guide rails 31. The supports for their rails 21 are positively coupled to a toothed rack 22 at least in the drive direction.

To ensure precise cooperation between the working elements 2and the needles 11 it is necessary to generate the shiftina movement with a very high degree of accuracy 9 and to transmit it free from play.

A toothed belt 41 is guided while under tension over two auide rollers 42, 425. The belt 41 has teeth 411 which are directed outwards and enaaae positively with the teeth 221 of the toothed rack 22 in the area of the lower run.

In the embodiment of the toothed belt drive shown in Figure 1. the toothed belt 41 is also provided with an internal tooth arrangement 412. One of the guide rollers 425 is at the same time a toothed drive wheel of a servomotor 46. The servomotor is an asynchronous motor 46 known per se, which may be digitally controlled with respect to rotational angle and returns high-resolution rotational anale signals in relation to time via a return line to a control unit 5 in order to control the movement made bv it.

A so-called digital/alternating current control unit 5, presently marketed and distributed under the concept "digitally controlled a.c. servo system", is provided for directly controlling this asynchronous motor 46. This control unit 5 has a processing unit (CPU), program storage 51 for computing programs for the controlled execution of work functions of the asynchronous motor 46, and storage for variable operands for calculation of drive programs for the asynchronous motor 46.

A target position signal for the appropriate working element 2 at a preset time is assumed by this alternating current control unit 5 from an overriding stored program control unit (SPS) 6. Usina the nreset variables and the stored computer programs, the alternatina current control unit 5 calculates the ontimum movement program for the asynchronous motor 46 and controls this according to this program- It is naturallv to be understood that electronic power amplifiers known Der se are included in this control process.

Figure 5 shows a speed/time graph as an example of three control programs A, B, C, of the asynchronous motor 46. The three different curves A, B, C show different programs for the execution a different strokes.

The computer programs stored in the storage unit 51 of the control unit 5 for the movement cycles may be adapted to various requirements with respect to the maximum speed, the maximum acceleration or other functionrelated parameters. Such requirements are often set when different thread materials are to be processed.

These programs may constantly be structured so that even on conclusion of the movement, there is still sufficient force to guide the working element 2 with absolute c-ertainty into the predetermined end position. Because of this optimum control of the movement cycle for the drive means. drive means or structural units 4 with verv small dimensions are sufficient for drive the workina elements 2.

The Darallel working elements 2, which are generally arranged very closely adjacent to one another and are often alianed on a uniform working plane cf. Fiaure 3 -, may be driven directly in the area of their guide on the frame.

Very long, space-taking and often deformable transmission members - e.along levers. long toothed racks 41 or chains or multi-ste-D aear pairs are disDensed with.

The toothed belt 41 provides precise transmission of the drive movement of the motor shaft onto the toothed rack 22 coupled to the rails 21 of the working elements 2.

It is essential for the structure of this motor that a large number of teeth of the toothed belt 41 engage with the drive wheel 425 of the asynchronous motor 46 as well as with the teeth 221 of the toothed rack 22. It is also important that the distance in the plane of the toothed belt 41 between these two areas of engagement in both directions is as short as possible and, moreover, 12 that the -toothed belt 41 has an exact guide there. In this way, the different elongations of the toothed belt 41, caused by the differentiated drive forces, or other causes of errors are practically eliminated.

This ensures that the drive movement of the asynchronous motor 46 is transmitted with high precision onto the respective working elements 2.

Figure 2 shows a further embodiment of the toothed rack drive by the example of the drive of the thread guide rail 21 in a flat weft knitting machine. In order to bring the force application between the tooth flanks of the teeth 221 of the rack 22 and the tooth f lanks of the teeth 441 of the toothed belt 41 as closely as possible to the so-called core of the toothed belt 41 the toothed belt 41 is provided with teeth on only one side. The run of the toothed belt 41 facing away from the toothed rack 22 is deflected in the form of a loop between two guide rollers 42, 43. The toothed drive wheel 44 of the asynchronous motor 46 is positioned in this loop to guide and drive the toothed belt 41. The teeth of this drive wheel 44 may cooperate positively in a sufficiently large angle area with the external tooth arrangement 411 of the toothed belt 41.

For support of the toothed belt 41 and/or the toothed rack 22 in the area of engagement between these 13 two components, adjustable support rollers 47 are provided for the toothed belt 41 and/or support rollers 48 for the toothed rack 22. These support rollers 47, 48 prevent any transverse forces which may be produced at the tooth flanks from causing deflection of the toothed belt 41 or toothed rack 22.

As can be seen from Fiaure 2, the drive unit 4 is comDosed of a motor 46, the supports for the guide rollers 42, 43 and the mountings for the support rollers. This structural unit 4 has a screw-on surface (not shown] for fastenina to the frame. A mountina Dlate 45 for all the mountings. which forms the frame of structural unit 4, is expediently provided with a housing 451 enclosing the entire toothed belt arrangement. The structural unit 4 may be allocated to a wide variety of structural assemblies or workina elements 2.

In flat weft knitting machines, for example, a larae number of Darallel thread guide rails 21 must be subiected to different strokes at a wide variety of times, and their end positions exactly defined. Since the structural unit 4 has a relatively small length independent of the stroke to be executed, these structural units 4 may be very closely staggered in the drive direction of the thread guide rails 21. If the structural units 4 of closely adjacent thread guide rails 14 21 are staggered one behind the other in drive direction, then it is possible to accommodate a very large number of such units in a verv narrow sDace.

These extremely small and low-mass transmission elements allow hiah sDeeds at the lowest forces of gravity.

For the drive of sinker cams 202 in flat weft knittina machines, it is sufficient if the structural unit 4 is secured to the suDDort for the guide rail for the sinker cam SUDDOrt, which may be swung transversely to the machine lonaitudinal axis in the usual manner. The toothed rack.22 is then fastened to the sinker cam connector rail to coonerate with the toothed belt 41 of the structural unit 4. Hence, large mass transmission elements may also be dispensed with in this case for the drive movement of the sinker cams 202. The small drive motors 46, which may therefore be used in this case, permit a clear reduction in the power consumption of the entire machine.

In particular in inlay pattern machines, where a very large number of thread guide rails 2 must be driven and stopped with a very high degree of precision, the control of the motor 46 according to the invention in conjunction with the force transmission to the working elements 2 according to the invention results in a clear is increase-.in the operating speed. It is practically possible, in this special case, to operate at the same speeds as were previously possible in flat weft knitting machines with a small number of thread guides.

Even with warp knitting machines, where the given threads do not need to be sunk, effects are achieved with the drive means according to the invention which were not possible previously with other mechanical devices. The optimised control program of the servomotor 46 in association with the free-from-play and error-free, lowmass transmission of the drive ensures a substantial degree of quietness of operation even in the case of extremely variable and high-stroke pattern repeats.

z 16 List of Reference Numbers Used 1 needle bar 11 needles 2 working element 201 thread guide 202 sinker cam 21 rail (support) 22 toothed rack 221 - teeth 3 mounting 31 guide rail 4 structural unit (drive unit) 41 toothed belt 411 - teeth external 412 - teeth internal 42 guide roller 425 drive wheel 43 guide roller 44 drive wheel mounting plate 451 housing 46 asynchronous motor 461 power transmission 462 return line 17 47 support rollers (toothed belt) 48 support rollers (toothed rack) alternating current control unit 6 storage programmed control (SPS) A, B, C, curves 19 18

Claims

1. Drive means for a knitting machine with working elements capable of reciprocal movement between defined positions parallel to a needle bar; said drive means comprising an asynchronous servomotor actuated by a programmable control unit providing target position signals to transmit rotational movement to a toothed rack carrying at least one of the working elements and a further control unit which has program stores for computer programs for calculating movement cycles from the target position signal data; wherein the servomotor has a toothed drive wheel meshing with a run of a toothed belt guided between guide rollers or between a guide roller and the toothed wheel parallel to the toothed rack with the toothed belt also meshing with the teeth of said toothed rack.

2. Drive means according to Claim 1, wherein the toothed belt is only provided with external teeth and the run of the toothed belt is deflected in the form of a loop between two guide rollers and partly around the drive wheel of the motor between the guide rollers.

3. Drive means according to Claim 1, wherein the toothed belt is provided with internal and external teeth, the internal teeth meshing with the toothed wheel 19 and the external teeth meshing with the toothed rack and the toothed belt is entrained around a guide roller and the drive wheel of the motor.

4. Drive means according to any one of Claims 1 to 3, wherein the drive motor and the guide roller or rollers are mounted with the toothed belt on a common mounting plate to form a structural unit.

5. Drive means according to Claim 4. wherein the structural unit also has a housing and an additional toothed belt guide, which is provided with recesses and with support rollers.

6. Drive means according to any one of Claims 1 to 5, wherein the further control unit is an alternating current control unit which is further provided with a processing unit, storage for variable operands, an input for receiving information from the firstmentioned control unit with pattern programs. an output connected to said drive motor, and a return line for receiving angle pulse sequences.

7. Drive means for a knitting machine substantially as described with reference to, and as illustrated in, Figure 1 or Figure 2 of the accompanying drawings or -Figure 1 or 2 as modified by Figure 3 or 4 of the accompanying drawings.

8. A knitting machine with working elements in the form of thread guides for flat weft knitting carried on guide rails provided with structural unit search with its own control utilizing drive means according to any one of the preceding claims; wherein the structural units of adjacent thread guide rails are staggered in relation to one another in the drive direction of the guide rails.

9. A knitting machine with working elements in the form of sinker cams for flat weft knitting carried on guide rails provided with structural units each with its own control utilizing drive means according to any one of Claims 1 to 7 with the associated toothed rack secured to a connector rail disposed between each two sinker cams.

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